FIG. 1 shows the structure of a slide switch of this type disclosed in Japanese Utility Model Application Publication No. H4-101611. In this example, the slide switch includes a fixed plate 11 placed in a buckle apparatus and a movable contact 12 attached to the fixed plate 11.
Three fixed contacts 13 to 15 are formed on the fixed plate 11; the fixed contact 13 positions on one side in the width direction of the fixed plate 11 and extends across both ends of the fixed plate 11. The fixed contact 14 positions on the other side in the width direction of the fixed plate 11 and extends from one end to a midpoint in the fixed plate 11. The fixed contact 15 positions on the other side in the width direction of the fixed plate 11 and extends from the midpoint to the other end of the fixed plate 11.
The movable contact 12, which includes blade springs, has a pair of feet 12a on both ends in the width direction and the feet 12a have L-shaped holding parts 12b, which bends so as to get close to each other. An opening 12c is formed at the center of the movable contact 12 and a pair of arms 12d and 12e extend in the longitudinal direction of the foot 12a from one side of the opening 12c. 
The movable contact 12 is slidably attached to the fixed plate 11 with the holding parts 12b in contact with the undersurface of the fixed plate 11 at both ends in the width direction of the fixed plate 11 and the pair of the arms 12d and 12e in contact with the fixed contacts 13 to 15. In FIG. 1, reference numeral 16 indicates an ejector of the buckle apparatus that slides when the tongue is inserted and reference numeral 17 indicates a compressed coil spring that urges the ejector 16 in a direction in which the tongue is removed.
A projection 16a of the ejector 16 positions in the opening 12c of the movable contact 12 and the ejector 16 is mated into the movable contact 12, and the movable contact 12 slides when pressed by the ejector 16. The arm 12d of the movable contact 12 is constantly in contact with the fixed contact 13 regardless of the slide position of the movable contact 12. The arm 12e makes contact with the fixed contact 14 or the fixed contact 15 depending on the attachment state of the tongue. This can be used to determine whether the tongue is removed from or inserted and mated into the buckle apparatus.